The present invention relates to lamps with reflecting mirrors and image projecting apparatus. In particular, the present invention relates to a lamp with a reflecting mirror used as a light source of a liquid crystal projector or a light source of image projecting apparatus such as a digital micromirror device (DMD) projector.
Image projecting apparatus such as liquid crystal projector devices are known as a means for magnifying and projecting images such as characters and figures to display the images. Such image display devices (or image projecting apparatus) need a predetermined optical output, so that reflecting-mirror-equipped lamps including high intensity discharge lamps (HID lamps) exhibiting high luminance are, in general, widely used as light sources. With widespread use of projectors, brighter and smaller projectors have been in demand.
FIG. 8 schematically shows a cross-sectional configuration of a prior art reflecting-mirror-equipped lamp 1000 for a projector. The reflecting-mirror-equipped lamp 1000 shown in FIG. 8 includes: a high pressure discharge lamp 1150; and a reflecting mirror 1300 provided with a front glass 1330. The high pressure discharge lamp 1150 is, for example, a high pressure mercury lamp operating with alternate current and includes: a luminous bulb 1100; and a pair of sealing portions 1101 respectively extending from both ends of the luminous bulb 1100. A luminous material (mercury) 1105 is enclosed in the luminous bulb 1100. A pair of opposed electrodes 1102 is placed in the luminous bulb 1100. The electrodes 1102 are connected to molybdenum foils 1103 located inside the respective sealing portions 1101. The molybdenum foils 1103 are connected to external leads 1104. The lamp 1150 equipped with the reflecting mirror 1300 is housed in a lamp house 1400, thereby constituting a lamp unit 1000.
One of the sealing portions 1101 of the lamp 1150 is equipped with a base 1200. The base 1200 is inserted into a neck portion 1306 of the reflecting mirror 1300 and fixed thereto with cement or the like. The base 1200 is electrically connected to one of the external leads 1104 extending from an end of the sealing portion 1101, so that an end of the base 1200 serves as a terminal LA of the high pressure discharge lamp 1150. The other external lead 1104 extending from the sealing portion 1101 located toward the wide opening of the reflecting mirror 1300 serves as a terminal LB of the high pressure discharge lamp 1150. The terminals LA and LB are joined to respective outward-drawn lead wires (cables) 1204a and 1204b by welding. The outward-drawn lead wires 1204a and 1204b are connected to a pin 1250 to be a terminal of the lamp unit 1500.
FIG. 9A is a perspective view schematically showing the lamp unit 1500 shown in FIG. 8. FIG. 9B is a cut-away perspective view schematically showing a projector body 1600 in which the lamp unit 1500 is placed. The configurations shown in FIGS. 8, 9A and 9B are disclosed in the prior art section in Japanese Laid-Open Publication No. 2002-6695.
As shown in FIG. 9B, the lamp unit 1500 is placed in the projector body 1600. Specifically, the pin 1250 provided on the lamp unit 1500 is inserted into a plug 1252 provided on the body 1600, and then a lid 1630 is attached to the body 1600. When the lamp unit 1500 is placed in the body 1600, the lamp unit 1500 is electrically connected to a ballast (not shown) provided within the body 1600. The ballast allows the lamp 1150 of the lamp unit 1500 to start and illuminate.
A cooling fan 1610 is provided at the rear of the lamp unit 1500 placed in the body 1600. An optical system using the lamp 1150 as its light source and a system (main system) for displaying an image by controlling the optical system are provided within the body 1600. Light emitted by the lamp 1150 passes through the optical system and a projecting lens 1620 and then is projected onto a screen where an image is produced.
As a projector is downsized and fabricated at lower cost, a reflecting-mirror-equipped lamp also needs to be downsized and fabricated at lower cost. Therefore, attempt has been made to produce the reflecting-mirror-equipped lamp with no base. The present inventors made a prototype of a reflecting-mirror-equipped lamp with no base and operated the lamp, to find that various problems arise or might arise. FIGS. 1A and 1B schematically show a configuration of the prototype of the reflecting-mirror-equipped lamp with no base made by the present inventors. FIG. 1A shows a reflecting-mirror-equipped lamp 1001 with no base. FIG. 1B shows a connection portion 20 in which an external lead 1104 and an outward-drawn lead wire 1204a are joined to each other, in an enlarged manner.
As shown in FIG. 1A, since the reflecting-mirror-equipped lamp 1101 has no base, the outward-drawn lead wire 1204a cannot be joined to a base by welding. In the example shown in FIG. 1B, the external lead 1104 and the outward-drawn lead wire 1204a are connected to each other via a nickel (Ni) sleeve 12 by welding. More specifically, the external lead 1104 is inserted into the Ni sleeve 12 so as to be in contact with the outer edge of the connection portion 20, and then the external lead 1104 and the Ni sleeve 12 are welded together at a relatively low temperature. Thereafter, the Ni sleeve 12 and the outward-drawn lead wire 1204a made of, for example, a Ni—Mn alloy are welded together, thereby the external lead 1104 and the outward-drawn lead wire 1204a are connected to each other. This technique is adopted because it is difficult to carry out a technique of wrapping the outward-drawn lead wire 1204a around the external lead 1104 or a technique of directly joining the outward-drawn lead wire 1204a and the external lead 1104 together by welding.
In the case of wrapping the outward-drawn lead wire 1204a around the external lead 1104, these components are not welded together. Accordingly, electrical connection (electrical continuity) between the outward-drawn lead wire 1204a and the external lead 1104 is incomplete. As a result, a discharge might occur at the connection portion 20, so that it is difficult to adopt the wrapping technique. In addition, molybdenum, which constitutes the external lead 1104, has a property of recrystallizing and becoming brittle under high temperatures, so that it is technically difficult to directly join the external lead 1104 and the outward-drawn lead wire 1204a to each other by welding. Therefore, a technique capable of welding the external lead 1104 and the outward-drawn lead wire 1204a together at low temperature, i.e., a technique of welding via the Ni sleeve, is adopted.
However, the Ni sleeve 12 and the outward-drawn lead wire 1204a are welded together by spot-welding, so that the contact area is small (almost a point contact). Accordingly, if a stress is applied to the outward-drawn lead wire 1204a, there arises a problem that the outward-drawn lead wire 1204a is easily detached from the connection portion 20. In particular, since the outward-drawn lead wire 1204a is exposed to the outside, the stress is easily applied thereto. As a result, the outward-drawn lead wire 1204a is often detached. In addition, the external lead 1104 and the Ni sleeve 12 are also welded together by spot-welding. Accordingly, if a stress is applied to the Ni sleeve 12 exposed to the outside, the Ni sleeve 12 is moved and detached from the welded portion. That is to say, the welding strength at the connection portion 20 is low, so that there is a problem that the welded portion is often separated by handling during assembly.
Furthermore, there found a problem that since the tips of the external lead 1104 and/or the outward-drawn lead wire 1204a are/is exposed to the outside because of the absence of a base as shown in FIG. 1B, the tip serves an antenna to generate a strong noise especially upon the application of a high-pressure pulse at the start of operation. In particular, a projector using a full digital device such as a DMD is vulnerable especially to noise, so that noise is a serious problem. In addition, since the tip of the wire is exposed to the outside, injury is likely to occur in replacing a lamp. Therefore, it is necessary to make a contrivance not to have users replace the lamp by themselves. With respect to the lamp unit, a configuration in which an opening of the lamp unit is made small so as to prevent a finger or the like from being easily inserted thereinto from the outside needs to be taken into consideration. However, such a configuration is disadvantageous especially for cooling in a lamp with a small reflecting mirror, resulting in another problem.
In addition, in the case of the lamp with a small reflecting mirror, the temperature at the neck portion 1306 is prone to increase, so that oxidation develops rapidly if the connection is made by welding. As a result, there arises a problem of a short lifetime. Now that the lifetime of lamps has been extended to, for example, 2000 hours or more thanks to the improvement of a fabrication technology or the like, it is necessary to eliminate shortening of the lifetime due to the reasons described above.